The development of thin, compact and highly automated cameras as described, for instance, in U.S. Pat. Nos. 3,750,551; 3,744.385; 3,731,608; and 3,714,879 has been seen to have generated a concomitant need for a flat and compact battery source of power capable of operating a variety of electrical control instrumentalities having somewhat specialized power requirements. For instance, the battery must have a relatively high current output capacity for powering a motor driven film processing and reflex optics cocking assembly as well as electrically automated shutters incorporating electromagnetic drive devices and the like. Inasmuch as these instrumentalities are regulated by logic circuitry, requisite voltage levels must be sustained by the batteries during the noted current drains. A flat multicellular pile structure is particularly suited for providing a requisite low internal impedance battery. As described in U.S. Pat. No. 3,543,662, preferably, the thin battery is mounted within a film cassette assemblage and takes the shape of one film unit thereof. In consequence of this combined battery power supply-film supply arrangement, the compactness and thinness of a resultant foldable camera may be optimized.
For practical utilization in combination with a photographic film product, for instance, to form the composite cassette assembly described above, the thin batteries must not only be amenable to economic high volume production techniques, but also must exhibit a very high reliability. Such reliability is mandatory inasmuch as the batteries are packaged as an integral part of the film cassette assemblage and any dysfunctions on the part of the battery component thereof well may result in the wasting of the entire film cassette or pack.
To achieve requisite low unit costs in producing such thin batteries, the industry heretofore has looked to techniques as described in U.S. Pat. No. 3,708,349, wherein wide, continuous and multizoned webs of the sheet type components of the batteries or piles are manipulated along a production line to somewhat simultaneously form a plurality of cells and composites thereof. Following deposition of substantially all electrochemically active materials upon the wide web, select portions thereof are slit and sheared and manipulated into registry and, ultimately sealed and sheared transversely of web movement to form discrete battery units. These discrete units then are packaged as a component of film cassette assemblages whereupon they are forwarded to retail distribution channels.
When such multizone, wide web-type high volume production battery assembly techniques are utilized, it is necessary that electrically conductive web-type components of the battery pile structures serve as carriers within the assembly system. For instance, electrically conductive materials such as metal and/or carbon impregnated polymeric sheet are utilized respectively as external current collectors and electrode supporting intercell connectors. When employed within a multizone wide web production scheme, these web-type conductive materials are combined with electrochemically active materials thus forming coupled active cell structures which may develop voltage phenomena along the production line. Such voltages may have the effect of derogating from battery performance. Further, the battery structures necessarily evolved from this form of wide-web assembly require a shearing of superposed conductive and insulative layers to evolve discrete battery structures. This inherently results in a flat battery geometry wherein the edges of adjacent conductive sheets and of intermediately disposed insulating separator-seal structures are arranged in vertical alignment. In carrying out thermal peripheral sealing of such structures, considerable care must be taken to avoid disturbing the laminar peripheral edges. In the absence of such care, adjacent electrically conductive sheet components may flow under heat and pressure to edge short the structure. To avoid such effects, heat-pressure operations are carried out inwardly a select distance from the peripheries from the battery structures. This practice carries the distinct disadvantage of reducing the effective area of the edge seals, the quality of such seals being of considerable importance to battery reliability as well as to achieving to acceptable manufacturing yields.
Proper performance of the seals within flat batteries represents a critical aspect of their utility. For instance, the flat batteries at hand are not compressively packaged in containers as is typical with batteries manufactured heretofore. To provide requisite flatness, the peripheral extent of the batteries requiring sealed integrity is much larger than conventional container structured batteries. The seals now contemplated must be continuous about the entire periphery of the batteries and must operate to retain adequate moisture within the electrochemical environment of the batteries and exclude environmental gases such as oxygen and the like. Further, it is desirable that seals provide a modicum of outgassing of effluvia generated within the battery, for instance, hydrogen in a LeClanche system.
Another technique for fabricating the above-described flat batteries provides for multicell pile buildup upon a continuous thin, sheet-type electrically insulative carrier. Described in detail in copending application for U.S. Pat. Ser. No. 478,106, by L. Bruneau, entitled Flat Battery and Manufacture Thereof, filed June 10, 1974, and assigned in common herewith, through the use of this discrete placement fabrication technique separator or seal elements for the batteries can be dimensioned so as to extend beyond the electrically conductive polymeric sheet components defining each cell. As a consequence, the occasion for the occurrence of edge shorting effects and the like during manufacture are greatly diminished and consequent manufacturing yields are improved. For any of the above-described techniques of manufacture however, edge sealing using heat and pressure necessarily result in a diminution of seal area. For instance, the metallic externally disposed current collector and terminal sheets of the structures necessarily warp under heat and pressure effects often occasioning a displayed formation or geometry of components about the battery peripheries. These effects are encouraged by a heretofore necessary sealing procedure wherein sealing or contact with each multicell battery unit during fabrication is limited to a zone residing inboard of the outer peripheral edges of the entire battery structure.